Refractory ceramic



Nov. 5, 1935. J. M. M KINLEY AL 2,019,618

' REFRACTORY CERAMIC Filed Sept. 25, 1933 3 Rate of 716M22 Jaw/ 09?feoar 2 aS/zrmkaye 222 percent Loss in wezy/zr as percent 0/ any/ha!plastic 60 in X, 4

j 152 wen ford;

Patented Nov. 5, 1935 UNITED STATES PATENT OFFICE REFRACTORY CERADIICApplication September 25, 1933, Serial No. 690,883

6 Claims. (Cl. 10611) The present invention relates to an improvement inthe manufacture of refractory ceramic articles such as fire-brick,furnace-lining material and the like, made substantiallyfromargillaceousmaterials such as clay.

One of the objects of the invention is to improve the green stre g h offreshly formed or molded dry ceramic articles, to overcome ,cracke ingduring the drying of the articles, and to' enhance the strength of thefinished fired products.

Another object of the invention is to decrease the porosity offire-brick and furnace linings or to enablethe production of products ofa given density without resorting to raw materials of 1 the usual degreeof comminution.

.A further object is to permit a' wider time i v and temperature rangeduring the firing of refractory argillaceous products, atthe same timebringing about an earlier glass or mineral phase during thefiringperiod.

Still afurther object of the invention to improve generally the physicalproperties of firebrick and fumace-lining material by employing inconnection with its manufacture a reagent consisting essentially ofsodium aluminate, par- 'ticularly the type known as sodiummeta-aluminate, the formula of which is NazAlzoi.

Other objects of the invention will become apparent fromthe'detaileddescription to follow hereinbelow and from the claimsappended to the present specification as well as from an examination ofthe drawing submitted herewith. In the -drawing,Fig.'-1 is a graphshowing the from the use of this reagent can be better visualized; andFig. 2 is a graph showing the diminution of the shrinkage 'on firingargillaceous ceramics when using sodium aluminate therein.

In its simplest embodiment, the invention 0011- cerns" itself withaprocess in which sodium aluminate, either .dry or in. solution, isadded to argillaceous raw ,materials of the type usually employed in themanufacture of refractory ceramic ware," and with the products resultingfrom the practice of the said process.

This invention relates intimately to the pro-- duction. of a unique and'novel structure in'clay ceramic .ware, in silica ceramic ware, andin'ware 1 which may be composed essentiallyof clay and silica. Thisstructure, which 'our invention producesin such wares, contributes novelanddesired physical properties to these products and the proportions ofthis addition may be greatly decreased, and in some practice theproportions also contributes beneficial'results in the nature of anenhancement of the desired physical properties normally possessed bysuchwares. In ad-. dition to the beneficial improvements resulting inthe ultimate product, our invention also con- I tributes beneficialresults concerning all phases of the manufacturing process, thesummation of which results, in the ultimate product, in the productionof ware of increased quality, increased specific utility, and increasedrange of utility. 1

More specifically, this invention relates to the improvement of wares inwhich a normal low green strength and great friability contributes todimculty in processing and results in finished ware lacking, to agreater or less d gree desired qualities.

This invention further relates especially to were of a composition whichnormally requires a much higher firing temperature to produce qualitiesessential to satisfactory utility' value than is required by ourprocess.The process involved in bringing about these improvements consistsessentially in the addition' of a new and novel ingredient to ceramicmixtures such as are otherwise common and a usual to this type ofceramic ware. This material, namely sodium aluminate, having thespecified physical properties later enumerated, is mixed with theceramic mass or mixture-in suitable'q'uantities and in such a manner soas to be, for the purposes required, sufii'ciently therein disseminated.The method of admixture employed may be any which is suitable to-themanufacturing process involved and the quantity added will depend uponthe physical properties or the ceramic mass or mixture involved. In theusual practice, the sodium aluminate addition will not comprise morethan one-twentieth part of the total weight of the mixture, and in somepractice of this addition may begreatly increased.

The following, however, composes an absolute essential of thespecifications of our invention: The sodium aluminate-must be in theform of a compound, fully and completely formed according to thespecifications hereinafter given, before L admixture with any of theceramic mixtures or masses in which it is desired to obtain the uniqueand-beneficial results which we have discovered and claim. We have foundthat in order to obtain these beneficial results there must be a Jointand cooperating action of the elements of sodium aluminate, which canonly be obtained by adding these elements in the form of the definitelyspecified compound The addition of the separate elements of sodiumaluminate, eithe; by themselves or combined separately or together withother elements in natural or synthetic combinations, we have proved bylong and exhaustive experimentation do not produce the novel andbeneficial efiects that are obtained'by the addition of the hereinafterspecified soduim aluminate.

We have further found that the several ele' ing, but the properties ofthe resulting finished product vary definitely from those propertiesproduced by sodium aluminate used as such; and that no other compound orcompounds comprised of the separate elements of sodium a'luminate, andno other compound and either or any of the separate elements of sodiumaluminate, can be introduced into a ceramic mixture or mass such as weare concerned with and result in producing all of, the novel andbeneficial effects which are produced by sodium aluminate throughout theprocess of manufacturing or attain the summation of improvementsresulting from the introduction of sodium aluminate.

Hence, specifically, our' invention consists of the addition of sodiumaluminate to ceramic mixtures comprised of clay, silica, or clay andsilica and commonly associated ingredients, it being an essential ofthis invention that the sodium aluminate addition be made in such amanner and insuch quantity as to produce thorough mixture anddissemination throughout the ceramic mass or mixture and to produce, tothe desired degree,

the peculiar structure resulting from sodium aluminate additions to suchceramic mixtures or masses, and that the sodium aluminate comprisingsuch addition shall have the following specified physical properties: Itshould consist 1 essentially of pure sodium meta-aluminate, Na2Al2O4,containing but a slight excess of sodium hydroxide or sodium carbonate.It should be completely or nearly completely soluble in water.

Wezhavefound that as a result of the additions of such specified sodiumaluminate, our process fully developes the following effects which havebeen found to be in themselves unique, novel and of great utility, andto contribute, in part or whole, either severally or in combination, toan ultimate product, unique, novel, and of great utility:

(a) Produces controlled coalescence of related grain particles,resulting from a seeming plastic flow produced by the addition of sodiumaluminate.

This result is plainly visible in the finished articles, which whenpolished to a plain surface exhibit a higher gloss and even whenexamined microscopically show a decided decrease in porosity whencompared with similar ceramic ware -made from the same raw materials butwithout the addition of the sodium aluminate.

(b) Diminishes common or usual shrinkage strains.

This is brought'out by the slower drying rate.

Slower drying allows the material to adjust itself better, therebyavoiding internal strains and 5 stresses. Obviously this will contributeto greater dry strength. Referring for the moment to Fig. 1, which is agraphical representation of the amount of weight lost by the productswhen dried at 55 C., this shows the percentage of weight lost plottedagainst time expressed in hours and compares a ceramic mix containing noadded sodium aluminate (curve No. 1), 3 sodium aluminate added in theform of a solution thereof in cold water (curve No. 2), and 3% end of 10hours the percentage loss compares as follows: 10%,6% and 4.6%, while atthe end of 24 hours the first curve shows that the material ispractically dry", the second curve shows a loss in weight of 9.5% andthe third of 7.9%. Thus also, it takes about 46 hours for the materialmade with the sodium aluminate to dry completely. This is, however, anadvantage rather than a disadvantage, for this gradual and even dryinginsures a more homogeneous green ware which has considerably greaterstrength.

(0) Increased green strength of all wares concerned without lowering theultimate fusion range of the finished fired articles. In order to provethis point, the following tests were made:

Test A.-4000 grams of a clay known in the ceramic art as Draucker clay,"previously passed through a 30 mesh screen, was mixed with 18% of itsweight (720 grams) of distilled water, and the resulting plastic masswas molded into test-bars 6"x1x1", and these were allowed to dry untilin an atmosphere maintained at 0. there was no further loss in weight.Simultaneously another portion of the same mass was molded into theshape of pyrometric cones and 50 into 1" cubes. The two latterforms wereemployed for other tests to described further on.

All of these test pieces, 1. e., the'bars, cones and added to the clay,the purpose being to give the sodium aluminate full time to get intoequilibrium condition in solution. The same kind of test bars, cones andcubes weremade from the resulting clay mass, and these were likewisedried to substantially constant weight at 50 C.

Test C.,The ingredients, again consisted of 4000 grams of the Drauckerclay, and 720 grams of tempering water in which there had been dispersed21.09 grams of very finely ground aluminum oxide (A1203) and 24.36 gramsof chemically pure sodium carbonate (NazCOa) The amount of thesechemicals employed was determined from an analysis of the sodiumaluminate employedin as sodium atoms and aluminum atoms a'reconcerned.The mixture of these chemicals with the 720 grams of water was likewiseallowed to stand for minutes before being incorporated with the clay.Test bars, cones and cubes were made in exactly the same manner asdescribed in con- I nection with Tat A, so that the resulting productswould be strictly and accurately comparable.

The following tests were applied to produced in Tests A, B and C: l

1., Transverse strength of green or unfired bars: These were made on atypical cross-breaking machine and are expressed as in terms of themodulus of rupture,.i n lbs. per sq. inch.

2. Drying shrinkage:--Expressed as per cent. of original.

3. Friabilityz-Expressed as the number of -blows of a 250 gr. weightfalling 5 cm., which.

were required to split the -1" dry unfired cubes.

4.'Pyrometric'cone equivalent (PCE): Comparison of the fusion values ofthe small. cones formed from the green materials with those of standardcones. Portions ,ofthe shapes resulting from each experiment were firedthrough aperiod of 48 'hours to an ultimate temperature of 1285 C.

The following tests were then applied:

5. Transverse strength of fired bars.

6. Total shrinkage of fired bars. v

7. Apparent specific gravity of fired bars.

8. Percent. porosity of fired bars.

9. Per cent. absorption. 1

Determinations 7, 8 and 9 were made in accordance with the testing"methods described on pages 33 and 34 of Specifications and MethodsofTest for Refractory Materials, published 1932 by theAmerican Society forTesting Materials.

The following results were obtained:

Test A Test B Test 0 l No addition With sodi- With alumi- I of sodium umaluminum hyaluminate note droride and sodium carbonate Green modulus ofrupture 78. 40 134. 90 70. 55 Dry shrinkage 3. 0% 3. 4. 0% 'grigbigty 2and 1 3 and 4 2 and l Fired modulus oi rupture"... 2027 16 Totalshrinkage 9. 0% Fired shrinkage 7. 5. 5% 5. Apparent sp. gr 2.592 2.6062.599 Per cent. porosity 28. 29 24. 26.29 Water absorption 10. 90 9. 10.11

It will thus be seen that the sodium aluminate addition resulted in a72.1% increase in dry or green strength, 16.66% increase in dryingshrinkage, decrease in friability values, allowing 1 to 2 more impacts,cone or more increase in P. C. E. value, average fired modulus ofrupture 25% higher than the minimum obtained with no. ad-

dition and 8.5% higher -than the average obtained I with no addition, adecrease in total shrinkage of 10%, a decrease in firing shrinkage of21% slightly increased apparent specific gravity,

14.2% decrease in the per cent. volume of open pores, and 14.7% decreasein per cent. water ab- 'sorption.

A similar comparison of values shows that the addition of the equivalentconstituents of sodium aluminate (i. e., the aluminum hydroxide andsodium carbonate) resulted in a 10% decrease in dry or green strength,33.3% in drying shrinkage, equal friability values, t cone decrease inP. C. E. value, average fired modulus of rupture the shapesapproximately equaling the value obtained with no addition, 10% decreaseintotal shrinkage, 28.5% decrease in firing shrinkage,

nearly equal apparent specific gravity, 7.07% decrease in per cent.volume of open pores, and

7.24% decrease in per cent. water absorption.-

Bars with no addition were badly warped in firing so that fired modulusof rupture values cannot be taken as true values. They arranged betweenthe values given. The other two series gave uni- Many of the form valuesthroughout the series. bars-of Test C blistered badly on the edges onfiring. This was due to soda migration, which, however, was notappreciably evident in the sodium aluminate series, Test B.

Tabulation showing relative increases and decreasesin values obtained inTests B and C as compared with those obtained in Test A (d) Permitsincrease in grain-size of aggregate without a corresponding increase inporosity.

(e) Permits a decrease ofporosity of the fired ware without alterationof the normal grainsize. Thus, in comparing batches made with and wereobtained:

Treated Untreated Test Pt Test Qt Teat'Pu 'DestQu tlon' 1oz: 16.3092.809 2280 8egmvity an? 2.551" 2.584 2.58? Apparentdensity .2031 2.1281.994 1.994

(f) Produces higher ultimate fusion value as expressed in P. C. E.equivalent. Thus, for example, a commercial batch was made as follows:

40% by weight of a plastic bond clay of the "type generally known asQueens run soft," passed through a 12 mesh screen; 40% by weight ofthesame, passed through a 20 mesh screen: 20% of grog, ground was topermit all topass of time, such as. from four to six minutes, for

the grinding operation was merely for the purpose of obtaining athorough incorporation of through a 12 mesh screen; making '100 parts;

, 40 without sodium aluminate, the following results shrinkage value of1.7%.

carried, i. e., from 2100 to 2300 F., as previous experience with thepresent invention had demonstrated that the ware containing the sodiumaluminate could safely be fired at the lower temperature. This,incidentally, was also an advantageaccruing from the use of the sodiumaluminate.

When comparing the products made with the sodium aluminate and thosemade without it, it was found that the former yielded a denser ware. Thefollowing table shows the results:

Ware with Ware withsodium out sodium aluminate aluminate Porosity l6. 8%22. 8% Specific gravity 2. 557 2. 584 Apparent density 2.128 1. 994

In order to exhibit the advantages of sodium aluminate to overcome asfar as possible the firing shrinkage, attention is now directed to Fig.2 and to the following commercially made batches of a refractorypatching cement. In order to have material upon which to base acomparison, two exactly similar batches were made, one of these howeverbeing without the addition of the sodium aluminate. These two batcheswere as follows:

T Treated with U sodium aluminate Untreated Kentucky grog 70'7. Kentuckysemi-hard clay- 20 Kentucky plastic clay.--" l0 g Sodium aluminate 1part per 100 of the None.

' above mixture. Water ll-l3 parts 11-13 parts.

The shaping of the material, in actual practice, is'of course omitted,as the material is sold in moist condition to be applied to the furnacewalls that are to be repaired. For the purposes of this test, however,test bars were formed, dried and fired. Pyrometric cones were likewiseprepared and tested. Fig. 2 shows graphically how the treated sample Tfirst showed a firing shrinkage between 1 6001F. and about 2660 F. quitecom parable to that of the untreated sample U, but then there is amarked change in direction of the curve, so that by the timea'temperature of 2840 F. has been reached the total shrinkage, which wasover 2 at 2660 F., has been diminished, by expansion during theintervening temperature range, to 0.5%; At'the same temperature, i. e.,2840" F., the untreated sample still showed a shrinkage of 2.5%, andeven when the latter sample was fired to 3100 F. it still had a finalThis effect can only be explained by the formation of a very definitetype of glass phase from the sodium aluminate,

probably by its interaction with constituents of the clay, and that thisphase by filling up the pores between the particles of the ceramicrefractory mass prevents its shrinking any further, v

and by its own expansion practically equalizes the previous contractionso that the final shrinkage is but 0.5%. This is a great advantage andan entirely unexpected and valuable result. The changes in dimensionsare plotted on Fig. 2.

The pyrometric cones made from these same batches'of material comparedas follows:

Sample '1' P. c. E.=32.5 Sample U ...P. C.-E.=31.5 to 32 Crushingstrength of fired were in lbs. per sq. in.

Sodium aluminate added Nnnn It might also be mentioned in thisconnection that by reason of increased green crushing strength morebricks can be set upon each other in the firing kilns, thus increasingtheir capacity.

In numerical values this compares with a limit I of 9 bricks high foruntreated ware as against a head as high as 20 i'or material treatedwith 1% of sodium aluminate. A further advantage of the increasedcrushing resistanceis that there is less marring evident on the firedbricks, such as is usually caused by indentations made on the lowerlayers by the weight of the bricks set thereon.

This recital of advantages could be considerably extended, but it isbelieved that enough has been given in the form of actual determinednumerical data to prove beyond peradventure that there are many andoutstanding advantages accruing from the incorporation of sodiumaluminate with clay in the production of refractory articles therefrom..In connectionwith the recitation of the above advantages, the formulasgiven are those of commercially made batches as well as of batches madeparticularly to determine accurately numerical differences betweenordinary refractories made merely from clay and those made with clay andsodium aluminate.

Asa still further example, commercial batches were produced in anotherof the plants available to the inventors, using the following basicproportions:

Parts- Calcined Pennsylvania flint clay (grog) 30 lennsylvania semi-hardclay 20 Pennsylvania plastic clay l0 "Bats (ground fire-brlck) 40' Tothis was added enough water to yield a plastic mass suitable forhand-molding into firebrick. Besides an untreated batch, batchescontaining the following additions of sodium aluminate were made and theware carried through the same operations of forming, drying, and firing,all at the same temperature and general con ditions, so that the resultsare strictly comparable:

Sodium aluminate added v Porosity P. C. E. Spalling test quenchings. Nottested. 12 quenchings. Not tested.

The porosity as well as the spelling tests were carried out strictly inaccordance with the directions for making'such tests as describedin the1932 edition of Specifications and Methods of Test for RefractoryMateria, of the American Society for Testing Materials. In reporting thespalling tests, the tabulation refers to the time when the firstcracking-off 'of pieces from the test piece occurred after previousheating and quenching. From the above table it will also be.

apparent that there is a decrease in porosity proportional to theincrease in the amount of sodium aluminate added. This is to beexpected,

and further corroboratesthe effects observable by visual inspection withthe naked eye as well as under magnification.

The present invention is broadly applicable to the various types ofargillaceous refractory ware, and it is desired to protect it by LettersPatent in accordance with the subjoined claims:

What is claimed is,

1. The process of producing highly-heat resistant, strong firebrickexhibiting marked decrease in porosity, great crushing strength,resistance to spelling and diminished firing shrinkage, which comprisesmixing fire-clay with ag- 5 gregates and an amount of sodium aluminate Isubstantially'equal to from about 1% to about 5% of the weight of theclay, and water to form a plastic mass, forming said mass into shapes,and drying and firing the same. i

2. A firebrick comprising substantially parts of clay, 20 parts ofpreviously fired clay, and 2' parts of sodium aluminate.

3. A firebrick or the like comprising 30 parts of flint clay, 20 partssemi-plastic clay, 10 parts 15.

plastic clay, 50 parts of ground brick-bats, and from to 1 parts ofsodium aluminate.

4. A firebrick comprising from to 99% of fired clay and from 1 to 2% offired sodium aluminate. I

5. The'process-of making refractory firebrick which comprises mixingclay with water and from about 1% to 5% of sodium aluminate to form a

